The lack of satisfactory brightness is often a concern for electrophoretic display devices. Total internal reflection inevitably would occur with an electrophoretic display device because such a display device usually has components of a high refractive index. Due to the components having a higher refractive index (e.g., about 1.5) than the air (which has a refractive index of about 1) surrounding the device, some of the scattering light from the display panel may reflect off the display front surface and back to the display device by total internal reflection. This total internal reflection phenomenon may result in a loss of about 30-50% of the scattering light, thus causing reduction in brightness of the display device.
To improve the brightness of a display device, a luminance enhancement structure may be laminated onto the viewing side of a display device to reduce the loss of brightness due to total internal reflection and to redirect some of the incident light towards the viewer. Unfortunately, the performance of such a luminance enhancement structure may be affected by the thickness of the substrate layer such as a polyethylene terephthalate (PET) layer, present between the display device and the luminance enhancement structure. Although efforts have been made to reduce the thickness of the PET substrate, the results achieved so far are not entirely satisfactory.